Prediction of residual stress distributions for single weld beads deposited on to SA508 steel including phase transformation effects

Abstract

The sensitivity of residual stress distributions in bainitic-martensitic steel welds to the transformation strains that arise when austenite decomposes on cooling has been assessed by examining the predictions of three models for a simple bead-on-plate configuration. These cover the following scenarios: case I, no phase transformations; case II, transformations with volume change effects only; case III, transformations with volume change effects and associated Greenwood-Johnson transformation plasticity. Austenite decomposition was predicted by implementing Kirkaldy's reaction rate equations as a subroutine in the finite element code Sysweld, eliminating the need for a continuous cooling transformation diagram. Predicted residual stresses were then compared and rationalised alongside measurements obtained by neutron diffraction and the contour method. It was found that serious errors in predicting the location and magnitude of the peak stresses occurred if transformations were not included, while cases II and III gave similar results generally in agreement with the stress maps. Indeed, the trends in the experimental results were intermediate between cases II and III. Differences between the models and the potential for further improvements are discussed.

The role of microstructure in the stress relaxation and tempering of laser clad Ti–6Al–4V

“…In analogy to welding processes that use filler material, this stress is created by the thermal profile of the laser in this region as it cools from its molten form [11]. Figure 3 shows that the clad layer has a martensitic structure, which when formed exerts a compressive stress on the lattice of the material [12], thus reduces the magnitude of any tensile residual stress present in the transforming material at the temperature at which the transformation occurs, which is around 530 o C for Ti-6AL-4V depending on the cooling rate [13]. Further into the substrate the tensile stresses decrease and then increase again.…”

Materials science at the diffractometer STRESS-SPEC at FRM II

“…The austenite to bainite (volume expansion in steel) transformation during welding and subsequent cooling reduces the stress in the weld, but shifts the peak stress to just the border of the heat affected zone (HAZ), the extend of which is determined by the heat input and welding speed, respectively. Data from similar experiments at STRESS-SPEC [2] have been used to develop models for prediction of residual stress distribution in ferritic steel welds [3].…”

Modelling Residual Stress and Phase Transformations in Steel Welds

“…The estimation of welding residual stresses in thick-section ferritic steel has been less successful than in austenitic stainless steel, largely due to the complexities associated with the solid state phase transformations that occur in multipass welding [1][2][3][18][19][20][21][22]. To predict residual stresses in ferritic steels, a phase transformation kinetics model is therefore required for prediction of microstructure evolution.…”